Very recently, communication apparatuses such as portable wireless appliances have been considerably popularized, and requirements for making these communication apparatuses more compact have been expected. In connection with these compact requirements, antennas have been required to be built in the communication apparatuses. Conventionally, as this sort of antenna units, for instance, one antenna unit is described in a patent publication 1. That is, as shown in FIG. 10, the above-described antenna unit is constructed as a built-in antenna by arranging a non-power feeding element 102 over a power feeding element 101 in such a manner that any current is not induced on a circuit board 103 in order to prevent characteristic deteriorations caused by adverse influences given from human bodies. It should be understood that reference numeral 104 in FIG. 10 indicates a power feeding line.
However, the conventional built-in antenna has a demerit. That is, since radiation toward the human body direction is large, the conventional built-in antenna may be adversely influenced by the human body due to the directivity thereof, and since large loss may be produced during telephone communications, gains of the built-in antenna may not be improved. Under such a circumstance, in order to improve the gains during the telephone communications, it is desirable to cause the conventional built-in antenna to have such a directivity having a direction opposite to the human body.
Under such a circumstance, portable wireless appliance-purpose antenna units capable of achieving high gains and also capable of broadening frequency bands thereof have been proposed (refer to, for instance, patent publication 2). That is, as indicated in FIG. 11, a portable wireless appliance-purpose antenna unit includes a circuit board 201, a line-shaped power feeding antenna element (power feeding element) 202, and a plate-shaped non-power feeding antenna element 203. The circuit board 201 is employed so as to arrange thereon various sorts of circuits of the portable wireless appliance. One end portion of the line-shaped power feeding antenna element 202 is connected to any one board plane of the circuit board 201 via a power feeding point (feeder point). The plate-like non-power feeding antenna element 203 is arranged opposite to any other board plane of the circuit board 201, and is operated as a reflector under such a condition that an electric length of this plate-like antenna element 203 along a longitudinal direction thereof becomes nearly equal to a ½-wavelength thereof. In accordance with such an antenna unit, since the plate-like antenna element (second antenna) 203 having an electromagnetic coupling effect with respect to the power feeding antenna element (first antenna) 202 is operated as the non-power feeding element, the broad frequency band and the high gain of this conventional antenna unit can be realized.    Patent Publication 1: JP-A-2001-244715    Patent Publication 2: JP-A-2004-32242